Knudsen Number

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

Knudsen number, abbreviated Kn, is a dimensionless number that is used in fluid dynamics to determine what type of analysis should be used to model an object moving through a fluid. It is defined as the ratio of the molecular mean free path length to a representative physical length scale. This calculation determines the Knudsen number, the length or the lambda value based on your inputs.

Knudsen Number Formula

\(\large{ Kn = \frac{ \lambda }{ l } }\)


\(\large{ Kn }\) = Knudsen number

\(\large{ l }\) = length

\(\large{ \lambda }\) (Greek symbol lambda) = mean free path

Solve for:

\(\large{ l = \frac{ \lambda }{ Kn } }\)

\(\large{ \lambda = Knl }\)